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Plasmid R100 was found to have two genes, designated pemK and pemI, that were responsible for its stable inheritance during cell division. They are located near the region that is essential for autonomous replication. Under conditions that inhibit replication of R100 derivatives, the plasmid containing these pem genes gave only a few segregants in viable cells and increased the number of nonviable cells in the population, suggesting that a product from the pem region stabilized the plasmid by killing plasmid-free segregants. Inactivation of one of the two translational open reading frames in the pem region caused the loss of the killing function, and thus, the open reading frame is a gene designated pemK, which encodes the killing factor. The coexistence of the pem+ plasmid with a high-copy-number plasmid carrying the other open reading frame inhibited stabilization, and thus, the second open reading frame is a gene designated pemI, which encodes the inhibitor which might control the killing function of pemK. It is likely that the two open reading frames were transcribed from a promoter. There were no significant homologies in DNA sequences between the pem gene of R100 and the genes previously shown to be responsible for the stable inheritance of the other plasmids.

Fertility factor F confers bacterial conjugation, a process which involves at least 20 tra genes. Resistance plasmids such as R100, R6-5, and R1 have homology with F in the tra region. Conjugal transfer of these plasmids is, however, repressed, while transfer of F is constitutive. Repression of R transfer is due to the existence of the two genes, called finO and finP; constitutive transfer of F is believed to be due to a lack of finO in F. In this paper, we report the identification and DNA sequence of the finO gene of R100, encoding a protein of 21,265 daltons. We show that F does actually encode finO, but the gene has been inactivated by insertion of IS3. Lederberg and Tatum (Nature [London] 158:558, 1946), who discovered sexuality in bacteria, may have had an Escherichia coli K-12 strain harboring such an finO F factor, which facilitated the generation of recombinant progeny useful for genetic analysis of bacteria and established the foundation for molecular genetics.

This paper proposes a ring element for the stress analysis of mitred bends, which is an extension of ring elements for pipe bends proposed by the present authors. Since accurate treatments of continuity conditions on the connecting lines between straight pipe segments are employed and strain-displacement relations derived from the general thin shell theory with shear strains are considered, the present method can be applied to problems of mitred bends of complex configurations under general loading conditions. Shape functions are developed by trigonometric functions and Hermitian polynomials of second order in the circumferential and longitudinal directions, respectively. This finite element method requires fewer number of degrees of freedom for the same accuracy than the conventional shell elements.

The creep behaviors of pipe bends under in-plane bending are studied by the use of the simplified ring element method. The typical two loading cases are studied; (a) constant in-plane moment, and (b) constant in-plane rotation. The present paper investigates (a) inelastic flexibility, (b) creep strain concentration, and (c) stress relaxation by considering effects of yielding on creep deformations. The numerical results verify the validity of the previous analytical methods for elastic stationary creep behaviors by Spence or Kachanov.

The sequence of oligonucleotides produced by the action of bleomycin and ferrous ion on double- and single-stranded DNA has been determined. In the presence of ferrous ion, bleomycin promotes cleavage at G-T and G-C sequences, while high concentrations of ferrous ion alone result in strand scission that is not base specific. In the presence of bleomycin and ferrous ion, pyrimidine bases located to the 3' side of guanosine are released preferentially and a low molecular weight product that forms a chromophore with thiobarbituric acid is produced from the deoxyribose moiety. Oligonucleotides produced by the action of bleomycin differ slightly in electrophoretic mobility from those produced by chemical or enzymatic cleavage. A model is proposed to explain the interactions of bleomycin with DNA.